1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a plasma display panel in which a ground area of a film-type front filter can be increased.
2. Background of the Related Art
A plasma display panel (hereinafter, referred to as a “PDP”) is adapted to display an image, including characters or graphics, by light-emitting phosphors emitting ultraviolet light of 147 nm, generated during the discharge of a gas, such as He+Xe, Ne+Xe or He+Ne+Xe. The PDP can be easily made thin and large, and it can provide greatly increased image quality with the recent development of the relevant technology. Particularly, a three-electrode AC surface discharge type PDP has advantages of lower driving voltage and longer product lifespan, as a voltage necessary for discharging is lowered by wall charges accumulated on a surface upon discharging, and electrodes are protected from sputtering caused by discharging.
FIG. 1 is a perspective view illustrating the structure of a discharge cell of a three-electrode AC surface discharge type PDP, in accordance with the background art. Referring now to FIG. 1, a discharge cell of a three-electrode AC surface discharge type PDP includes a scan electrode Y and a sustain electrode Z, which are formed on the bottom surface of an upper substrate 10, and an address electrode X formed on a lower substrate 18. The scan electrode Y includes a transparent electrode 12Y, and a metal bus electrode 13Y, which has a line width smaller than that of the transparent electrode 12Y and is disposed at one side edge of the transparent electrode 12Y. Further, the sustain electrode Z includes a transparent electrode 12Z, and a metal bus electrode 13Z, which has a line width smaller than that of the transparent electrode 12Z and is disposed at one side edge of the transparent electrode 12Z.
The transparent electrodes 12Y and 12Z, which are generally made of ITO (indium tin oxide), are formed on the bottom surface of the upper substrate 10. The metal bus electrodes 13Y and 13Z are generally formed on the transparent electrodes 12Y and 12Z and made of metal such as chromium (Cr), and serve to reduce a voltage drop caused by the transparent electrodes 12Y and 12Z having high resistance. On the bottom surface of the upper substrate 10, in which the scan electrode Y and the sustain electrode Z are placed parallel to each other, is laminated an upper dielectric layer 14 and a protective layer 16. The upper dielectric layer 14 is accumulated with a wall charge generated during plasma discharging. The protective layer 16 is adapted to prevent damage of the upper dielectric layer 14 due to sputtering caused during plasma discharging, and improve efficiency of secondary electron emission. As the protective layer 16 is generally formed of magnesium oxide (MgO).
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18, in which the address electrode X is formed. A phosphor layer 26 is applied to the surfaces of both the lower dielectric layer 22 and the barrier ribs 24. The address electrode X is formed on the lower substrate 18 in the direction in which the scan electrode Y and the sustain electrode Z intersect with each other. The barrier ribs 24 are formed in a stripe or lattice form to prevent ultraviolet and visible light, generated by discharging, from leaking toward adjacent discharge cells. The phosphor layer 26 is excited with an ultraviolet light generated during the plasma discharging to generate any one visible light of red, green and blue lights. An inert mixed gas is injected into the discharge spaces defined between the upper substrate 10 and the barrier ribs 24, and between the lower substrate 18 and the barrier ribs 24.
This PDP is time-driven with one frame being divided into a plurality of sub-fields having a different number of emission in order to implement gray scales of an image. Each of the sub fields is divided into an initialization period for initializing the entire screen, an address period for selecting a scan line and selecting a cell from the selected scan line, and a sustain period for implementing gray scales according to the number of discharging cycles. For example, if it is desired to display an image with 256 gray scales, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields SF1 to SF8, as shown in FIG. 2. Each of the sub-fields SF1 to SF8 is subdivided into the initialization period, the address period and the sustain period, as described above. The initialization period and the address period of each of the sub-fields SF1 to SF8 are the same every sub-field, whereas the sustain period increases in the ratio of 2n (where, n=0, 1, 2, 3, 4, 5, 6, 7) in each sub-field. In the PDP described above, a front filter is disposed on the upper substrate 10 in order to shield electromagnetic interference and also to prevent reflection of external light.
FIG. 3 schematically shows one side of a POP, in accordance with the background art Referring to FIG. 3, the PDP includes a panel 32 in which an upper substrate 10 and a lower substrate 18 are combined. A front filter 30 is disposed at the front of the panel 32. A cooling fin 34 is disposed at the rear of the panel 32. A printed circuit board 36 is attached to the cooling fin 34. A rear cover 38 is formed to surround the rear of the PDP. A filter support unit 40 connects the front filter 30 and the rear cover 38, and a support member 42 is disposed between the front filter 30 and the rear cover 38 to surround the filter support unit 40.
The printed circuit board 36 supplies driving signals to electrodes of the panel 32. The printed circuit board 36 includes various driving units (not shown). The panel 32 displays a given image according to the driving signal supplied from the printed circuit board 36. The cooling fin 34 dissipates heat generated from the panel 32 and the printed circuit board 36. The rear cover 38 serves to protect the panel 32 from external shock and also to shield electromagnetic interference (hereinafter, referred to as “EMI”) discharged from the rear side of the panel 32.
The filter support unit 40 electrically connects the front filter 30 to the rear cover 38. Such a filter support unit 40 grounds the front filter 30 to the rear cover 38, and also prevents EMI from being discharged laterally. The support member 42 supports the filter support unit 40, the front filter 30 and the rear cover 38.
The front filter 30 shields EMI and also prevents reflection of external light. For this, the front filter 30 includes an anti-reflection film 50, an optical characteristic film 52, a glass 54, an EMI shield film 56, and a near infrared (hereinafter, referred to as “NIR”) shield film 58, as shown in FIG. 4. Adhesive layers are formed between the films 50, 52, 54, 56 and 58 of the front filter 30, respectively, to provide adhesion among the films 50, 52, 54, 56 and 58. A black layer 60 is further provided at an upper edge of the front filter 30.
The anti-reflection film 50 prevents externally incident light from reflecting toward the outside again, thus improving the contrast of the PDP. This anti-reflection film 50 is formed on the surface of the front filter 30. The anti-reflection film 50 can be additionally formed on the rear of the front filter 30. The optical characteristic film 52 serves to lower transmittance of the red (R) and the green (G) light among light incident from the panel 32, and to improve an optical characteristic of the PDP by increasing transmittance of the blue (B) light.
The glass 54 serves to prevent the front filter 30 from being damaged due to external shock. In other words, the glass 54 supports the front filter 30 so as to prevent damage of the front filter 30 from external shock. The EMI shield film 56, shields EMI to prevent EMI, which is introduced from the panel 32, from being discharged externally. The NIR shield film 58 shields NIR discharged from the panel 32, and thus prevents NIR of over a given reference from being discharged externally so that signals transmitted using IR, such as signals from a remote controller, can be transmitted normally without interference. The black layer 60 defines a valid display region A/A of the panel 32, and also covers unnecessary, unsightly edge portions of the PDP module.
The front filter 30 is electrically connected to the rear cover 38 through the filter support unit 40, as shown in FIG. 5. This will be below described in more detail. The filter support unit 40 is connected to the rear of the front filter 30 at one lateral side of the front filter 30. The filter support unit 40 is electrically connected to at least one of the EMI shield film 56 and NIR shield film 58. That is, the filter support unit 40 connects the front filter 30 to the rear cover 38, thus shielding EMI and/or NIR.
The front filter 30, in accordance with the background art, uses a glass 54 having a size greater than the upper substrate of the panel 32, so as to prevent the front filter 30 from being broken due to external shock. However, if the glass 54 is included in the layers of the front filter 30, there is a disadvantage in that a thickness of the front filter 30 is enlarged. Further, if the glass 54 is included in the front filter 30, there are problems in that a weight is increased and the manufacture cost is also increased.
In view of these disadvantages, a film-type front filter 70 from which the glass 54 is removed has been proposed. FIG. 6 shows such a film-type front filter 70, in accordance with the background art. The film-type front filter 70 has the same size as the upper substrate of the panel, and includes an anti-reflection film 80, an optical characteristic film 82, an EMI shield film 86 and a NIR shield film 88. Adhesive films are formed between the films 80, 82, 86 and 88 of the film-type front filter 70, respectively, to provide adhesion among the films 80, 82, 86 and 88. The film-type front filter 70 further includes a ground face 72 formed at an edge region of the anti-reflection film 80, and a black layer 90 formed in a region, which is spaced apart from the ground face 72 by a given distance.
The anti-reflection film 80 is formed on a surface of the film-type front filter 70, and serves to prevent externally incident light from being reflecting externally again. This anti-reflection film 80 can be additionally formed at the rear of the film-type front filter 70. The optical characteristic film 82 lowers transmittance of the red (R) light and the green (G) light among light incident from the panel, and also improves an optical characteristic of the PDP by increasing transmittance of the blue (B) light.
The EMI shield film 86 shields EMI to prevent EMI incident from the panel from being discharged externally. The NIR shield film 88 serves to shield NIR incident from the panel. Such a NIR shield film 88 prevents NIR of over a given reference from being discharged externally, so that signals transmitted from a remote controller to the panel can be transmitted normally without interference. The ground face 72 is electrically connected to the rear cover 38, as shown in FIG. 3, through a filter support unit (not shown). The black layer 90 defines a valid display region A/A of the panel, and also covers unnecessary, unsightly edge portions of a the PDP module.
In the PDP having the above-described film-type front filter 70, the film-type front filter 70 is fabricated to have the same size as the upper substrate of the panel. Thus, the ground face 72 and the black layer 90 are formed at the same time. Due to this, there are disadvantages in that the area of the ground face 72 is reduced in size. The reduced size makes it difficult to achieve alignment between the film type front filter 70 and the upper substrate of the panel because spaces for forming the ground face 72 and the black layer 90 are insufficient.